Alternative models for Flower function in CG endocytosis. (A) Flower resides on intracellular vesicles and acts as a calcium channel. Flower-mediated efflux from these vesicles triggers endocytosis of CGs. (B) Flower-containing vesicles fuse with the plasma membrane at the IS. Flower in the plasma membrane recruits endocytic adaptor proteins such as AP-2 in a calcium-dependent manner to trigger endocytosis of CGs.